Duchenne muscular dystrophy (DMD) is a deadly childhood disease that affects both skeletal and cardiac muscles and for which there is no effective treatment or cure. The majority of patients with DMD and those with a milder form of the disease, Becker muscular dystrophy (BMD) develop progressive cardiomyopathy that eventually leads to death in 20 and 50% of patients, respectively. We propose a mechanism of dystrophic cardiomyopathy disease progression that is dependent on signaling through the transcription factor nuclear factor-kappaB (NF-?B). Our previous work has demonstrated the requirement for NF-?B signaling in dystrophic skeletal muscles, however the implications of NF-?B signaling in dystrophic cardiac muscle remain unknown. In the proposed studies, Aim 1 will evaluate the relevance of NF-?B in dystrophic cardiomyopathy. Dystrophin- deficient mice (mdx) will be used as a model to determine how early NF-?B becomes activated, the specific NF-?B signaling pathway involved (classical vs. alternative), and the identity of cell types expressing NF-?B in dystrophic hearts. EMSA analysis, NF-?B reporter mice, immunostaining, western blotting, kinase assays, and FACS analysis will be used to evaluate Aim 1. Aim 2 will determine the requirement for NF-?B signaling in disease development. Mdx mice deficient for NF-?B signaling in all cell types and specifically in cardiomyocytes will be evaluated for histological, functional, and gene expression differences compared to mdx mice without NF-?B ablation. Aim 3 will investigate the mechanism by which NF-?B promotes dystrophic cardiomyopathy. Real time RT-PCR will be performed on cardiomyopathy-related genes that are known targets of NF-?B. Genes will be placed in functional groups (eg: fibrotic, inflammatory, survival) to determine if NF-?B is mechanistically promoting cardiomyopathy by targeting a specific group of genes. Additionally, a genome- wide search for all NF-?B targets will be performed using ChIP-sequencing to ensure an unbiased approach for evaluating NF-?B signaling targets is undertaken. The completion of these aims will provide significant insight into the role of the NF-?B signaling pathway in cardiomyopathy, as well as the relevance for targeting this signaling modulator for the treatment of DMD and BMD.